Adam Osmayev, 31, the Chechen ringleader, reportedly confessed to planning the assassination of the Russian prime minister on the orders of Doku Umarov, the emir of the Islamist insurgency against Moscow's rule in the North Caucasus region.

The timing of the revelation by Kremlin-controlled media has however been seen as an electoral ploy by Mr Putin's allies to boost his image as a guarantor of stability battling shadowy foreign forces in the final week before the election, which he is expected to win.

The murder plot was allegedly exposed after the blast in Odessa on January 4, which was initially thought to be a domestic gas explosion. However, it transpired to be an accident during the preparation of an explosive device.

Channel One showed Osmayev in detention saying: "The ultimate aim was to travel to Moscow and try to assassinate Premier Putin." One of the men, Ruslan Madayev, 26, died in the blast but Ukrainian special forces seized a second, Ilya Pyanzin, 28, two days later. Osmayev, who was shown with blotches of green antiseptic covering wounds on his face, was captured at the beginning of February. The men had a laptop with several videos of Mr Putin's cortege travelling through Moscow on it.

Osmayev - who had reportedly been on a federal arrest warrant since 2007 - said they planned to detonate a tank mine to kill Mr Putin rather than use a suicide bomber, although Madayev had been prepared to become a martyr.

Mr Putin did not comment but his spokesman, Dmitry Peskov, confirmed the murder conspiracy was real.

Many commentators were sceptical of the plot - apparently exposed several weeks ago - suggesting it was either fabricated or at the least revealed at a convenient time for Putin.

Dmitry Oreshkin, a political scientist, said the "timely" appearance of the assassination plot was "a sign that the real leaders of Vladimir Putin's political apparatus – people from the FSB – are trying an old trick to mobilise public opinion using the logic: 'Enemies are all around us. We have just one decisive, effective, clever national leader who they are trying to destroy.'" Oreshkin said the electorate was expected to react by consolidating around Putin against the external threat, giving "a considerable boost to his ratings".

Channel One made a point of mentioning that Osmayev lived for several years in London, which is also home to Akhmed Zakayev, the Chechen rebel envoy whom Moscow has tried unsuccessfully to extradite.

An FSB (Russian Federal Security Service) operative showed videos of Putin's convoy found on Osmayev's computer. "These were in order to understand where the bodyguards sit and how many cars are escorting, from different angles and streets," he explained.